The proposed studies are continuations of investigations into the biological properties of SV40 early proteins. During the previous project period, we demonstrated the antigenic relatedness of the known SV40 early proteins to large T-antigen, detected the presence of large T-polypeptide in the plasma membrane of SV40-infectd and -transformed cells, demonstrated antigenic differences betweem T-polypeptides in nuclei and plasma membranes, showed that a cytoplasmic form of SV40 T-antigen induced by an SV40-adenovirus 7 hybrid virus inhibited the nuclear migration of wild-type T-antigen, and delineated a difference in phosphorylation between nuclear and cytoplasmic forms of T-antigen. It proposed to further characterize the membrane-associated T-antigen and to define the regions of the T-polypeptide which confer various functional activities to the molecule and which govern its movement to specific intracellular compartments. The role of the membrane-bound T-antigen in TSTA activity will be defined, as will its ability to interact with cellular proteins, such as non-viral T-antigen and major histocompatibility complex products. Attempts will be made to transfer the mutated gene which codes for cytoplasmic T-antigen from the hybrid virus back to SV40. These studies will expand our understanding of the biological functions of virus-induced early proteins in transformed cells and will provide important insights into the process of neoplastic transformation in general.